Method of fatigue control

ABSTRACT

This invention relates to a method comprising (a) employing a composition comprising (i) an oil of lubricating viscosity; and (ii) a salt of a nitrogen containing poly(meth)acrylate and a phosphorus acid ester; and (b) lubricating a gear with such composition resulting in control of gear fatigue.

FIELD OF INVENTION

The present invention relates to a method for imparting fatigue control into a gear.

BACKGROUND OF THE INVENTION

It is known that a gear box suffers from fatigue through prolonged use. The main types of gear fatigue are micropitting, spalling, and pitting. However, when additives are employed to control micropitting there is a tendency for spalling and pitting performance to be reduced. Conversely, additive technologies which control spalling and pitting performance often reduces micropitting performance.

U.S. Pat. No. 6,586,375 discloses a lubricating composition containing a salt of a polyacrylate and at least one phosphorus ester.

It would be advantageous to have a method of general fatigue control for gear. The present invention provides one method of fatigue control.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: Surface employing the composition of Example 1.

FIG. 2: Gear surface Obtained Employing the Composition of the Reference Example.

SUMMARY OF THE INVENTION

The invention provides a method comprising (a) employing a composition comprising (i) an oil of lubricating viscosity; and (ii) a salt of a nitrogen containing poly(meth)acrylate and a phosphorus acid ester; and (b) lubricating a gear with such composition resulting in control of gear fatigue.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides a method comprising (a) employing a composition comprising (i) an oil of lubricating viscosity; and (ii) a salt of a nitrogen containing poly(meth)acrylate and a phosphorus acid ester; and (b) lubricating a gear with such composition resulting in control of gear fatigue.

Oil of Lubricating Viscosity

The lubricating oil composition includes natural or synthetic oils of lubricating viscosity, oil derived from hydrocracking, hydrogenation, hydrofinishing, and unrefined, refined and re-refined oils and mixtures thereof.

Natural oils include animal oils, vegetable oils, mineral oils and mixtures thereof. Synthetic oils include hydrocarbon oils, silicon-based oils, and liquid esters of phosphorus-containing acids. Synthetic oils may be produced by Fischer-Tropsch gas-to-liquid synthetic procedure as well as other gas-to-liquid oils. In one embodiment the polymer composition of the present invention is useful when employed in a gas-to-liquid oil. Often Fischer-Tropsch hydrocarbons or waxes may be hydroisomerised.

In one embodiment the base oil is a polyalphaolefin including a PAO-2, PAO-4, PAO-5, PAO-6, PAO-7 or PAO-8. The polyalphaolefin in one embodiment is prepared from dodecene and in another embodiment from decene.

Oils of lubricating viscosity may also be defined as specified in the American Petroleum Institute (API) Base Oil Interchangeability Guidelines. In one embodiment the oil of lubricating viscosity comprises an API Group I, II, III, IV, V, VI or mixtures thereof, and in another embodiment API Group II, III, IV or mixtures thereof. In another embodiment the oil of lubricating viscosity is a Group III or IV base oil and in another embodiment a Group IV base oil. If the oil of lubricating viscosity is an API Group II, III, IV, V or VI oil there may be up to about 40 wt % and in another embodiment up to a maximum of about 5 wt % of the lubricating oil an API Group I oil present.

The oil of lubricating viscosity in one embodiment is present from about 60 wt % to about 99.5 wt % of the composition and in another embodiment from about 75 wt % to about 97 wt % of the composition. The oil of lubricating viscosity may be used alone or in combination.

Nitrogen Containing Poly(meth)acrylate

The nitrogen containing poly(meth)acrylate in one embodiment has weight average molecular weight (M_(w)) in the range from about 10,000 to about 350,000, in another embodiment from about 12,000 to about 200,000, in another embodiment from about 15,000 to about 150,000 and in another embodiment from about 20,000 to about 120,000. Here and elsewhere in the specification and claims range and ratio limits may be combined. Polydispersity of the nitrogen containing polymers (abbreviated PDI for polydispersity index) values (Mw/Mn), where Mn denotes number average molecular weight, range from about 1.2 to about 5, or from about 2 to about 4.

In one embodiment, the ester groups of the (meth)acrylate ester monomers contain from about 1 to about 40 carbon atoms. The (meth)acrylate ester monomers are obtained by, for example, esterification of (meth)acrylic acid, or the anhydride or an acyl halide thereof, or by transesterification of (meth)acrylic esters, usually lower alkyl esters (lower alkyl contains 1 to about 5 carbon atoms), most often, methyl esters. As noted hereinabove, the ester alkyl groups are generally derived from an alcohol or mixture of alcohols. Alcohols which are useful include methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, octyl alcohol, 2-ethylhexyl alcohol, isooctyl alcohol, nonyl alcohol, isononyl alcohol, decyl alcohol, isodecyl alcohol, undecyl alcohol, 2-tert-butylheptyl alcohol, dodecyl alcohol, tridecyl alcohol, 2-methyldodecyl alcohol, capryl alcohol, lauryl alcohol, myristyl alcohol, pentadecyl alcohol, palmityl alcohol, stearyl alcohol, octadecyl alcohol, nonadecyl alcohol, eicosyl alcohol, cetyleicosyl alcohol, stearyleicosyl alcohol, docosyl alcohol. In one embodiment the (meth)acrylate ester monomers may be used alone or in combination.

In another embodiment, the nitrogen-containing polymers are derived from (a) from about 60% to about 99.9% by weight, in another embodiment from about 80 to about 99% by weight of alkyl (meth)acrylate ester monomers containing from about 8 to about 40 carbon atoms in the alkyl group and (b) from about 0% to about 40% by weight, in another embodiment from about 1% to about 20% by weight of alkyl (meth)acrylate ester monomers containing from about 1 to about 7 carbon atoms in the alkyl group and (c) from 0% to about 40% by weight, in another embodiment from about 0% to about 20% by weight of one or more other comonomers such as a vinyl aromatic monomer, for example a styrenic monomer, such as styrene, alpha-methyl styrene, ring substituted styrenes, vinyl napthalenes, vinyl anthracenes. Alkyl methacrylate esters are particularly useful monomers. Alcohols which are useful for preparing ester (a) may be linear or branched and include n-octanol, 2-ethylhexyl alcohol, isooctyl alcohol, nonyl alcohol, isononyl alcohol, isodecyl alcohol or any of the commercially available mixtures of alcohols including including Neodol®25 commercially available from Shell, and other suitable alcohols including Lial®125, Alchem® 125, Alfol® 810, Alfol® 1214 and Nafol® 1620 are all commercially available from Sasol. Alcohols which are useful for preparing ester (b) include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, t-butyl alcohol, pentyl alcohol, hexyl alcohol and heptyl alcohol as well as cycloalkyl alcohols such as cyclopentyl alcohol and cyclohexyl alcohol.

In another embodiment, the nitrogen-containing polymers are derived from (d) from about 75% to about 94.9% by weight of alkyl (meth)acrylate ester monomers containing from about 12 to about 18 carbon atoms in the alkyl group and (e) from about 5% to about 24.9% by weight of alkyl (meth)acrylate ester monomers containing from 1 to about 4 carbon atoms in the alkyl group. In one embodiment alkyl methacrylate esters are used. Alcohols which are useful for preparing ester (d) may be linear or branched and include isodecyl alcohol or any of the commercially available mixtures of alcohols including Neodol®25 commercially available from Shell, and other suitable alcohols including Lial®125, Alchem® 125, Alfol® 810, Alfol® 1214 and Nafol® 1620 are all commercially available from Sasol. Alcohols which are useful for preparing ester (e) include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, isobutyl alcohol, n-butyl alcohol and t-butyl alcohol. In one embodiment the alcohols may be used alone or in combination.

In another embodiment, the nitrogen-containing polymers are derived from a mixture of alkyl (meth)acrylate ester monomers containing (f) from about 8 to about 24 carbon atoms in the ester group, or from about 12 to about 18 carbon atoms, or from about 12 to about 15 carbon atoms, and (g) from about 6 to about 11 carbon atoms, in another embodiment from about 8 to about 11 carbon atoms and in another embodiment about 8 carbon atoms and which have 2-(C1-4 alkyl)-substituents, and optionally, one or more monomers including (meth)acrylate esters containing from about 1 to about 7 carbon atoms in the ester group and which are different from (meth)acrylate esters (f) and (g), or vinyl aromatic compounds. The mole ratio of esters (f) to esters (g) in the copolymer ranges in from about 95:5 to about 35:65, from about 90:10 to about 60:40 or from about 80:20 to about 50:50. In one embodiment, the ester group in ester (f) contains branched alkyl groups. The branched alkyl group in one embodiment is present from about 2 to about 65% and in another embodiment from about 5 to about 60% of the ester groups. Alcohols which are useful for preparing ester (f) may be linear or branched. In one embodiment about 2 to about 65% of the alcohols are branched, and in another embodiment from about 5 to about 60% are branched. The branched alcohol in one embodiment contains from about 8 to about 24 carbon atoms and in another embodiment about 12 to about 15 carbon atoms. Mixtures of alcohols are commercially available and are useful. Examples of alcohols useful to prepare ester (f) include n-octanol, nonyl alcohol, decyl alcohol, n- and branched C12, C15, C16, and C22 alcohols, mixtures of alcohols, eg., Dobanol® 25, Neodol® 25, Lial® 125 and Alchem® 125, which have varying degrees of branching, for example from about 5% to about 50% branching, or more, and Alfol® 1214, which is substantially linear.

In one embodiment wherein the poly(meth)acrylate is prepared from a reaction of (a) from about 60% to about 99.9% by weight of alkyl (meth)acrylate ester monomers containing from about 8 to about 40 carbon atoms in the alkyl group and (b) from about 0% to about 39.9% by weight of alkyl (meth)acrylate ester monomers containing from about 1 to about 7 carbon atoms in the alkyl group and (c) from 0% to about 39.9% by weight of one or more other comonomers such as a vinyl aromatic monomer; (d) and a nitrogen containing monomer.

In one embodiment the poly(meth)acrylate is prepared from a reaction of (a) from about 75% to about 99.9% by weight of alkyl (meth)acrylate ester monomers containing from about 12 to about 18 carbon atoms in the alkyl group and (b) from about 5% to about 24.9% by weight of alkyl (meth)acrylate ester monomers containing from 1 to about 4 carbon atoms in the alkyl group and a nitrogen containing monomer.

In one embodiment the poly(meth)acrylate is prepared from a reaction of (meth)acrylate ester monomers containing (a) from about 8 to about 24 carbon atoms in the ester group and (b) from about 6 to about 11 carbon atoms in the ester group and which have 2-(C₁-4 alkyl)-substituents; (c) a nitrogen containing monomer; and (d) optionally a (meth)acrylate ester containing from about 1 to about 7 carbon atoms in the ester group and which are different from (meth)acrylate esters (a) and (b) or a vinyl aromatic compound.

Nitrogen Containing Monomer

The nitrogen-containing polymers of this invention are derived from nitrogen containing monomers. The nitrogen containing monomer, in one embodiment, is present in an amount from about 0.1% to about 5% by weight and in another embodiment from about 1.5% to about 2.5% by weight. In another embodiment, the nitrogen containing monomer is present in an amount from about 1% to about 20% by weight and in another embodiment from 5% to about 10% by weight.

The nitrogen containing monomer may be any monomer that is capable of copolymerizing with (meth)acrylate monomers or is capable of being grafted onto poly(meth)acrylate polymers. In one embodiment the nitrogen containing monomer is an mono- or di-aminoalkyl (meth)acrylic amide or dialkyl amino alkyl (meth)acrylate such as a dimethyl amino alkyl (meth)acrylate. In one embodiment the alkyl group of dimethyl amino alkyl (meth)acrylate is propyl and in another embodiment ethyl.

The amide of a (meth)acrylic monomer for example, includes an acrylamide or a methacrylamide such as a hydrocarbyl substituted acrylamide or a hydrocarbyl substituted methacrylamide. In one embodiment the number of carbon atoms present in the hydrocarbyl group is 1 to 40, in another embodiment 1 to 20, in another embodiment 2 to 16 and in yet another embodiment 2 to 8.

In one embodiment the hydrocarbyl substituted acrylamide or a hydrocarbyl substituted methacrylamide includes monomers represented by formula (I):

wherein

Q is hydrogen or methyl, in one embodiment Q is methyl;

each R³ is independently hydrogen or hydrocarbyl group containing 1 to 8 or 1 to 4 carbon atoms;

each R⁴ is independently hydrogen or hydrocarbyl group containing 1 to 2 carbon atoms, in one embodiment each R³ is hydrogen; and

g is an integer from 1 to 6 or 1 to 3.

Examples of a suitable nitrogen containing monomer include a hydrocarbyl substituted acrylamide or a hydrocarbyl substituted methacrylamide, vinyl pyridine, N-vinyl imidazole, N-vinyl pyrrolidinone, and N-vinyl caprolactam, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, dimethylaminobutylacrylamide dimethylamine propyl methacrylate, dimethylaminopropylacrylamide, dimethylaminopropylmethacrylamide, dimethylaminoethylacrylamide or mixtures thereof. The nitrogen containing poly(meth)acrylate is from an amino alkyl (meth)acrylic amide, dialkyl amino alkyl (meth)acrylate or mixtures thereof. The nitrogen containing monomer may be used alone or in combination.

Phosphorus Acid Ester

As used herein the term phosphorus acid-ester means that the phosphorus acid is partially ester. As described above, the present invention relates to salts of nitrogen containing polymers. The salts of phosphorus salts are prepared from phosphoric acid esters. The salts are prepared by mixing enough phosphorus acid ester to neutralize at least all or a portion of the basic nitrogen present in the nitrogen containing copolymer. The mixture in one embodiment contains from about 0.5 parts to about 10 parts, in another embodiment from about 1 part to about 8 parts, in another embodiment from about 2 parts to about 6 parts by weight of phosphorus acid ester. In one embodiment the amount by weight of the nitrogen containing polymer is from about 99.5 parts to 90 parts, in another embodiment from 99 parts, to 93 parts and in another embodiment from 98 parts to 94 parts by weight nitrogen containing polymer. In one embodiment the phosphorus acid ester may be used alone or in combination.

In one embodiment, the phosphorus acid ester is a phosphorus acid ester prepared by reacting one or more phosphorus acids or anhydrides with an alcohol containing from about 1 carbon atom and in another embodiment from about 3 carbon atoms. The alcohol generally contains up to about 30, or up to about 24, or up to about 12 carbon atoms. The phosphorus acid or anhydride is generally an inorganic phosphorus reagent, such as phosphorus pentoxide, phosphorus trioxide, phosphorus tetroxide, phosphorus acid, phosphorus halide (e.g phosphorus trichloride), lower phosphorus esters, or a phosphorus sulfide, including phosphorus pentasulfide, and the like. Lower phosphorus acid esters generally contain from 1 to about 7 carbon atoms in each ester group. The phosphorus acid ester may be a mono- or di-hydrocarbyl phosphoric acid ester. Alcohols used to prepare the phosphorus acid ester include butyl, amyl, 2-ethylhexyl, hexyl, octyl, oleyl, and cresol alcohols. Examples of commercially available alcohols include Alfol® 810; Alfol® 1218; Alfol® 20+ alcohols; and Alfol® 22+ alcohols. Alfol® alcohols are available from Continental Oil Company. Another example of a commercially available alcohol mixtures are Adol® 60 and Adol® 320. The Adol® alcohols are marketed by Ashland Chemical.

A variety of mixtures of monohydric fatty alcohols derived from naturally occurring triglycerides and ranging in chain length of from about C₈ to C₁₈ are available from Procter & Gamble Company. These mixtures contain various amounts of fatty alcohols containing mainly 12, 14, 16, or 18 carbon atoms. An example is CO-1214 fatty alcohol. Another group of commercially available mixtures include the “Neodol®” products available from Shell Chemical Co. Examples include Neodol® 91 alcohols; Neodol® 23 alcohols; Neodol® 25 alcohols; and Neodol® 45 alcohols. In one embodiment the fatty alcohols may be used alone or in combination.

Examples of useful phosphorus acid esters include the phosphoric acid esters prepared by reacting a phosphoric acid or anhydride with cresol alcohols.

In another embodiment, the phosphorus antiwear/extreme pressure agent is a thiophosphorus acid ester or salt thereof. The thiophosphorus acid ester may be prepared by reacting a phosphorus sulfide, such as those described above, with an alcohol, such as those described above. The thiophosphorus acid esters may be mono- or dithiophosphorus acid esters. Thiophosphorus acid esters are also referred to as thiophosphoric acids.

In one embodiment, the phosphorus acid ester is a monothiophosphoric acid ester or a monothiophosphate. Monothiophosphates may be prepared by the reaction of a sulfur source with a dihydrocarbyl phosphite. The sulfur source may for instance be elemental sulfur. The sulfur source may also be a monosulfide, such as a sulfur coupled olefin or a sulfur coupled dithiophosphate. In one embodiment the sulfur is elemental sulfur. The preparation of monothiophosphates is disclosed in U.S. Pat. No. 4,755,311 and PCT Publication WO 87/07638, which are incorporated herein by reference for their disclosure of monothiophosphates, sulfur sources, and the process for making monothiophosphates. Monothiophosphates may also be formed in the lubricant blend by adding a dihydrocarbyl phosphite to a lubricating composition containing a sulfur source, such as a sulfurized olefin. The phosphite may react with the sulfur source under blending conditions (i.e., temperatures from about 30° C. to about 100° C. or higher) to form the monothiophosphoric acid or salt thereof.

In another embodiment, the phosphorus antiwear/extreme pressure agent is a dithiophosphoric acid, a phosphorodithioic acid or mixtures thereof. The dithiophosphoric acid may be represented by the formula (RO)₂PSSH wherein each R is independently a hydrocarbyl group containing from about 3 to about 30, or up to about 18, or to about 12, or to about 8 carbon atoms, or mixtures thereof. Examples R include isopropyl, isobutyl, n-butyl, sec-butyl, the various amyl, n-hexyl, methylisobutyl carbinyl, heptyl, 2-ethylhexyl, isooctyl, nonyl, behenyl, decyl, dodecyl, and tridecyl groups. Illustrative lower alkylphenyl R groups include butylphenyl, amylphenyl, heptylphenyl, etc. Examples of mixtures of R groups include: 1-butyl and 1-octyl; 1-pentyl and 2-ethyl-1-hexyl; isobutyl and n-hexyl; isobutyl and isoamyl; 2-propyl and 2-methyl-4-pentyl; isopropyl and sec-butyl; and isopropyl and isooctyl. In one embodiment the dithiophosphoric acid is a dihydrocarbyl dithiophosphoric acid. In one embodiment the phosphorodithioic is a dihydrocarbyl phosphorodithioic acid.

In one embodiment, the dithiophosphoric acid may be reacted with an epoxide or a glycol. This reaction product may be used alone, or further reacted with a phosphorus acid, anhydride, or lower ester. The epoxide is generally an aliphatic epoxide or a styrene oxide. Examples of useful epoxides include ethylene oxide, propylene oxide, butene oxide, octene oxide, dodecene oxide, styrene oxide, etc. Propylene oxide is used. The glycols may be aliphatic glycols having from 1 to about 12, or about 2 to about 6, or 2 or 3 carbon atoms, or aromatic glycols. Glycols include ethylene glycol, propylene glycol, catechol, resorcinol, and the like. The dithiophosphoric acids, glycols, epoxides, inorganic phosphorus reagents and methods of reacting the same are described in U.S. Pat. No. 3,197,405 and U.S. Pat. No. 3,544,465.

The following Examples P-1 through P-3 exemplify the preparation of useful phosphorus acid esters:

Example P-1

Phosphorus pentoxide (64 grams) is added at about 58° C. over a period of about 45 minutes to about 514 grams of hydroxypropyl O,O-di(4-methyl-2-pentyl)phosphoro-dithioate (prepared by reacting di(4-methyl-2-pentyl)-phosphorodithioic acid with about 1.3 moles of propylene oxide at about 25° C.). The mixture is heated at about 75° C. for about 2.5 hours, mixed with a diatomaceous earth and filtered at about 70° C. The filtrate contains about 11.8% by weight phosphorus, about 15.2% by weight sulfur, and an acid number of about 87 (bromophenol blue).

Example P-2

A mixture of about 667 grams of phosphorus pentoxide and the reaction product of about 3514 grams of diisopropyl phosphorodithioic acid with about 986 grams of propylene oxide at about 50° C. is heated at about 85° C. for about 3 hours and filtered. The filtrate contains about 15.3% by weight phosphorus, about 19.6% by weight sulfur, and an acid number of about 126 (bromophenol blue).

Example P-3

Alfol 8-10 (about 2628 parts, about 18 moles) is heated to a temperature of about 45° C. whereupon about 852 parts (about 6 moles) of phosphorus pentoxide are added over a period of about 45 minutes while maintaining the reaction temperature between about 45-65° C. The mixture is stirred an additional about 0.5 hour at this temperature, and is there-after heated at about 70° C. for about 2-3 hours.

The following examples relate to the phosphorus salts of nitrogen containing polymers as used in the present invention.

Example A

A reaction vessel is charged with about 95 parts of the polymer of Example N-1 and is heated to approximately about 60° C., about 3.5 parts of the product of Example P-2 is added dropwise with stirring. The addition is accomplished over about 30 minutes. The mixture is maintained at about 60° C. for about 1½ hours to obtain the desired product.

The following table contains additional examples of phosphorus salts of the nitrogen containing polymers. The examples are prepared as described in Example A. The amounts and the ingredients are specified in the table. B C D E F G H I J Polymer of — 95 — 96.5 — — — 98 — Ex N-1 Polymer of 94 — — — — 96.8 — — — Ex N-4 Polymer of — — 97 — 96.8 — 96.8 — 99 Ex N-6 Product of — — 3 — 3.2 — — 2 — Ex P-2 Di-methylpentyl — 5 — 1.8 — 3.2 — — — dithiophosphoric acid Product of 6 — — 1.7 — — 3.2 — 1 Ex P-3

The nitrogen salt of the containing polymers and the phosphorus acid esters may be used in lubricants or in concentrates. The concentrate may contain the sulfurized composition or other components used in preparing fully formulated lubricants. The concentrate also contains a substantially inert organic diluent, which includes kerosene, mineral distillates, or one or more of the oils of lubricating viscosity discussed below. In one embodiment, the concentrates contain from about 0.01% up to about 90%, in another embodiment from about 0.1% to about 80% and in another embodiment from about 1% up to about 70% by weight of the sulfurized combination of a fatty acid or ester and an olefin.

The salts of the nitrogen containing polymers and the phosphorus acid esters may be present in a final product, blend, or concentrate in any amount effective in lubricating compositions. In one embodiment the salts are present in the lubricating composition in an amount from about 0.5% up to about 40%, in another embodiment from about 1% up to about 35%, in another embodiment from about 2% up to about 30% and in another embodiment from about 3% up to about 25% by weight.

In one embodiment the invention provides a method comprising: (a) employing a composition comprising: (i) about 60 wt % to about 99.5 wt % of an oil of lubricating viscosity; and (ii) about 0.5 wt % up to about 40 wt % of a salt of a nitrogen containing poly(meth)acrylate and a phosphorus acid ester; and (b) lubricating a gear resulting in control of gear fatigue.

Additional Performance Additive

In one embodiment the method optionally includes at least one additional performance additive. The additional performance additive includes at least one of metal deactivators, detergents, dispersants, viscosity modifiers, friction modifiers, dispersant viscosity modifiers, extreme pressure agents, antiwear agents, antioxidants, corrosion inhibitors, foam inhibitors, demulsifiers, pour point depressants, seal swelling agents and mixtures thereof. In one embodiment the additional performance additives may be used alone or in combination.

The total combined amount of the other performance additive compounds present on an oil free basis ranges from 0 wt % to 25 wt % and in another embodiment 0.01 wt % to 20 wt % of the composition. Although one or more of the other performance additives may be present, it is common for the other additional performance additives to be present in different amounts relative to each other.

If the present invention is in the form of a concentrate (which may be combined with additional oil to form, in whole or in part, a finished lubricant), the ratio of the star-polymer of the invention and other optional performance additives in an oil of lubricating viscosity, to diluent oil including in the range of 80:20 to 10:90 by weight.

Antioxidants include a molybdenum dithiocarbamate, a sulphurised olefin, a hindered phenol, a diphenylamine; detergents include neutral or overbased, Newtonian or non-Newtonian, basic salts of alkali, alkaline earth and transition metals with one or more of a phenate, a sulphurised phenate, a sulphonate, a carboxylic acid, a phosphorus acid, a mono- and/or a di-thiophosphoric acid, a saligenin, an alkylsalicylate, a salixarate; and dispersants include N-substituted long chain alkenyl succinimide as well as posted treated version thereof, post-treated dispersants include those by reaction with urea, thiourea, dimercaptothiadiazoles, carbon disulphide, aldehydes, ketones, carboxylic acids, hydrocarbon-substituted succinic anhydrides, nitriles, epoxides, boron compounds, and phosphorus compounds.

Antiwear agents include compounds such as metal thiophosphates, especially zinc dialkyldithiophosphates; phosphoric acid esters or salt thereof; phosphites; and phosphorus-containing carboxylic esters, ethers, and amides; antiscuffing agents including organic sulphides and polysulphides, such as benzyldisulphide, bis-(chlorobenzyl) disulphide, dibutyl tetrasulphide, di-tertiary butyl polysulphide, di-tert-butylsulphide, sulphurised Diels-Alder adducts or alkyl sulphenyl N′N-dialkyl dithiocarbamates; and Extreme Pressure (EP) agents including chlorinated wax, organic sulphides and polysulphides, such as benzyldisulphide, bis-(chlorobenzyl) disulphide, dibutyl tetrasulphide, sulphurised methyl ester of oleic acid, sulphurised alkylphenol, sulphurised dipentene, sulphurised terpene, and sulphurised Diels-Alder adducts; phosphosulphurised hydrocarbons, metal thiocarbamates, such as zinc dioctyldithiocarbamate and barium heptylphenol diacid; may also be used in the composition of the invention.

The friction modifiers include fatty amines, esters such as borated glycerol esters, fatty phosphites, fatty acid amides, fatty epoxides, borated fatty epoxides, alkoxylated fatty amines, borated alkoxylated fatty amines, metal salts of fatty acids, fatty imidazolines, condensation products of carboxylic acids and polyalkylene-polyamines, amine salts of alkylphosphoric acids; viscosity modifiers including hydrogenated copolymers of styrene-butadiene, ethylene-propylene polymers, polyisobutenes, hydrogenated styrene-isoprene polymers, hydrogenated isoprene polymers, polymethacrylate acid esters, polyacrylate acid esters, polyalkyl styrenes, alkenyl aryl conjugated diene copolymers, polyolefins, polyalkylmethacrylates and esters of maleic anhydride-styrene copolymers; and dispersant viscosity modifiers (often referred to as DVM) include functionalised polyolefins, for example, ethylene-propylene copolymers that have been functionalized with the reaction product of maleic anhydride and an amine, a polymethacrylate functionalised with an amine, or styrene-maleic anhydride copolymers reacted with an amine; may also be used in the composition of the invention.

Additional performance additives such as corrosion inhibitors include octylamine octanoate, condensation products of dodecenyl succinic acid or anhydride and a fatty acid such as oleic acid with a polyamine; metal deactivators including derivatives of benzotriazoles, 1,2,4-triazoles, benzimidazoles, 2-alkyldithiobenzimidazoles or 2-alkyldithiobenzothiazoles; foam inhibitors including copolymers of ethyl acrylate and 2-ethylhexylacrylate and optionally vinyl acetate; demulsifiers including polyethylene glycols, polyethylene oxides, polypropylene oxides and (ethylene oxide-propylene oxide) polymers; pour point depressants including esters of maleic anhydride-styrene, polymethacrylates, polyacrylates or polyacrylamides; and seal swell agents including Exxon Necton-37™ (FN 1380) and Exxon Mineral Seal Oil (FN 3200); may also be used in the composition of the invention.

INDUSTRIAL APPLICATION

The invention is useful for gear fatigue control including at least one of micropitting, pitting, spalling and improved friction and/or gear change shift feel. The method is useful for a gear including a transaxle, a manual and an automatic transmission.

In one embodiment the invention provides a method comprising adding the composition described herein to a gearbox containing a gear and optionally a driveshaft (transaxle).

The following examples provide an illustration of the invention. These examples are non exhaustive and are not intended to limit the scope of the invention.

EXAMPLES Examples 1 to 10

A composition is prepared by blending about 90 wt % of group IV base oil with about 10 wt % of a salt of a nitrogen containing poly(meth)acrylate and a phosphorus acid ester prepared in Examples A-J.

Reference Example 1

Reference Example 1 is prepared by blending about 89.6 wt % of a group IV base oil in the presence of about 10 wt % of a commercially available polymethacrylate viscosity modifier and about 0.4 wt % of a separate oil soluble amine salt of a phosphorus antiwear agent.

Test 1: Pitting Test

A FZG pitting text is carried out employing C-type gears, at load 9 and at about 90° C. (also referred to as C/9/90 conditions) for over about 250 hours. The results obtained for pitting are rated from 0 to 2 for the pinion and wheel. Generally the lower the number indicates less micropitting with rating 0 equivalent to less than about 10% of surface micropitted; a rating of 1 is equivalent to about 10 to about 30% of the surface being micropitted and 3 has greater than about 30% of the surface micropitted.

The results obtained for the pinion and wheel rating for Example 1 is one and for Reference Example 1 is two. Images of the gear surface are shown in FIGS. 1 and 2 when the gear surface is lubricated using the composition of Example 1 and Reference Example 1 respectively.

Test 2: Friction Test

The friction ageing coefficient is measured by a variable speed reducer similar to the combination of Falex® Tester and LVFA® Tester. The test conditions are the variable speed reduced has an average speed of about 740 rpm, a load of about 350 Newtons and at about 120° C. The friction coefficient for Example 1 is continuous at about 0.08 over the length of the test. For Reference Example 1 the ageing coefficient decreased from about 0.1 to about 0.05 and was intermittently broken.

In summary the method of controlling gear fatigue employing a lubricant containing Example 1 to 10 has control over pitting, spalling, micropitting and improved friction and/or gear change shift feel relative to Reference Example 1. 

1. A method comprising (a) employing a composition comprising (i) an oil of lubricating viscosity; and (ii) a salt of a nitrogen containing poly(meth)acrylate and a phosphorus acid ester; and (b) lubricating a gear with such composition resulting in control of gear fatigue.
 2. The method of claim 1, wherein the phosphorus acid ester comprises a phosphorodithioic acid or a dithiophosphoric acid mixtures thereof.
 3. The method of claim 2, wherein the phosphorus acid ester is a dihydrocarbyl phosphorodithioic acid or a dihydrocarbyl dithiophosphoric acid containing about 3 to about 30 carbon atoms in each hydrocarbyl group mixtures thereof.
 4. The method of claim 1, wherein the poly(meth)acrylate is prepared from a reaction of of (a) from about 60% to about 99.9% by weight of alkyl (meth)acrylate ester monomers containing from about 8 to about 40 carbon atoms in the alkyl group and (b) from about 0% to about 39.9% by weight of alkyl (meth)acrylate ester monomers containing from about 1 to about 7 carbon atoms in the alkyl group and (c) from 0% to about 39.9% by weight of one or more other comonomers such as a vinyl aromatic monomer; (d) and a nitrogen containing monomer.
 5. The method of claim 1, wherein the poly(meth)acrylate is prepared from a reaction of of (a) from about 75% to about 94.9% by weight of alkyl (meth)acrylate ester monomers containing from about 12 to about 18 carbon atoms in the alkyl group and (b) from about 5% to about 25% by weight of alkyl (meth)acrylate ester monomers containing from 1 to aobut 4 carbon atoms in the alkyl group; and (d) a nitrogen containing monomer.
 6. The method of claim 1, wherein the poly(meth)acrylate is prepared from a reaction of of (meth)acrylate ester monomers containing (a) from about 8 to about 24 carbon atoms in the ester group and (b) from about 6 to about 11 carbon atoms in the ester group and which have 2-(C₁-4 alkyl)-substituents; (c) a nitrogen containing monomer; and (d) optionally a (meth)acrylate ester containing from about 1 to about 7 carbon atoms in the ester group and which are different from (meth)acrylate esters (a) and (b) or a vinyl aromatic compound.
 7. The method of claim 1, wherein the nitrogen containing poly(meth)acrylate is from an amino alkyl (meth)acrylic amide, dialkyl amino alkyl (meth)acrylate or mixtures thereof.
 8. The method of claim1 1, wherein the polymethacrylate has a weight average molecular weight in the range from about 10,000 to about 350,000.
 9. The method of claim 1, wherein the method of gear fatigue controls at least one of micropitting, pitting and spalling.
 10. The method of claim 1, wherein the oil of lubricating viscosity is a Group III or IV base oil.
 11. The method of claim 10, wherein the oil of lubricating viscosity is a Group IV base oil.
 12. A method comprising (a) employing a composition comprising (i) about 60 wt % to about 99.5 wt % of an oil of lubricating viscosity; and (ii) about 0.5 wt % up to about 40 wt % of a salt of a nitrogen containing poly(meth)acrylate and a phosphorus acid ester; and (b) lubricating a gear with the compostion resulting in control of gear fatigue. 